SIFT Principles of Helicopter Flight Questions and Answers 3

Question 1

What is 'vortex ring state' (settling with power) in helicopters?

Accepted Answer

A dangerous condition where the helicopter descends into its own rotor vortex, losing lift despite high power

Answer

A condition where the rotor vortex improves lift efficiency in a hover

Answer

A situation where the tail rotor enters a vortex from the main rotor

Answer

A condition caused by flying through the wake of another aircraft

Question 2

How does increasing altitude affect a helicopter's hover ceiling?

Accepted Answer

Higher altitude reduces the hover ceiling because thinner air requires more power to generate the same lift

Answer

Higher altitude improves hovering efficiency due to thinner air

Answer

Hover ceiling is unaffected by altitude until above 20,000 feet

Answer

Higher altitude increases hover ceiling because engines produce more power in thin air

Question 3

What is gyroscopic precession and how does it affect helicopter flight?

Accepted Answer

A force that causes a spinning rotor to respond to an applied force 90° later in the direction of rotation

Answer

The tendency of a spinning gyroscope to maintain its orientation in space, causing delayed control response

Answer

The precession of Earth's magnetic field affecting compass accuracy

Answer

The gradual movement of the rotor hub due to bearing wear

Question 4

What is 'dissymmetry of lift' in forward helicopter flight?

Accepted Answer

Unequal lift between the advancing and retreating sides of the rotor disc due to different airspeeds

Answer

Unequal lift between the main rotor and tail rotor

Answer

Difference in lift between the upper and lower surfaces of rotor blades

Answer

Unequal lift between the rotor disc center and outer tip areas

Question 5

What is the purpose of 'lead-lag' (drag) hinges on articulated rotor systems?

Accepted Answer

To allow blades to move fore and aft in the plane of rotation, reducing bending stress from Coriolis forces

Answer

To allow blades to flap up and down for dissymmetry of lift compensation

Answer

To control the pitch angle of each blade independently

Answer

To absorb vertical landing shock loads

Question 6

What is the 'H-V diagram' (Height-Velocity diagram) used for in helicopter operations?

Accepted Answer

A chart identifying dangerous combinations of altitude and airspeed where a safe autorotation landing may not be possible

Answer

A chart showing hover ceiling vs. outside air temperature

Answer

A diagram of helicopter control input movements

Answer

A graph of engine power vs. airspeed for performance planning